The dragqueen iphone app works without with no wifi or cell service. I like to walk up to the bow when we start putting out chain and mark the location of the anchor and then add offset from the location of the anchor. Its easy enough to test the app when you're out for a walk.

Something to consider is that gps apps eat battery. I keep my iphone plugged into a charging battery overnight.

Cheers, RickG


S/V Echoes, 2003 Beneteau 423
Grenada